Seismic Assessment Of Urban Elevated Bridges Based On Pushover Analysis

Urban bridge is an important hub of urban rail transit system.Once it is damaged in the earthquake,it will make the traffic system of the disaster area face paralysis, bring great resistance to emergency rescue and disaster relief.The closure of the bridge operation will impact economy in a large extent. So,the bridge structure seismic performance evaluation in design phas and the identification of bridge damage and the repairing technology after the earthquake are very significant. In recent years, the seismic performance evaluation based on the city overpass Bridges are relatively few.The traditional earthquake damage prediction method of bridge structural which is based on the statistics is feasible to the prediction of whole group bridges’s earthquake damage,but it is not applicable to a designated bridge. And the accuracy is far from enough especially for the high important coefficients bridges. The seismic damage assessment model of the bridge structure in the working statement has its disadvantages and limitations of the applicable scope. Especially,the deformation damage model which is based on the stiffness degradation and ductility index,cannot reflect the impact of low cycle fatigue.Basing on the existing bridge structure seismic performance evaluation methods, this article mainly carries out the following researches:This thesis introduces the basic concepts and theories of the Pushover analysis method.And also discusses mainly about the loading mode involved in the methods, this thesis finds out two difficulties involved in the load condition of the pushover analysis. This thesis also makes a detailed discussion on the displacement controlling method and load controlling method. It works out the master node and its control displacement which is related to target-displacement method selected in the analysis model.This thesis discusses the standards and principles of the structure’s earthquake damage hierarchies,and points out the blank of the classification of the bridge structure of earthquake damage at home and abroad.The earthquake damage hierarchies principle of the steel reinforced concrete frame structure is brought into the bridge structure field. The earthquake damage hierarchies standard of the steel reinforced concrete frame structure is made into detailes.This thesis explains the corresponding relationship between the damage index of the structure and its earthquake damage level.This thesis bases on the overpass bridges D ramp of Lanzhou city,caculates out the earthquake damage index of single pier and entire bridge in the different site conditions and different seismic intensity. The accuracy and practicality of the method is verified perfectly.This thesis comparatively analysis the results which are based on the single parameter and double parameters damage model.And it points out that the double parameters seismic damage model which is based on the factor of accumulation hysteresis energy dissipation is rationality and comprehensive. This thesis summarizes the advantages and limitations of seismic assessment method which is based on the pushover analysis.